G-IV crew reported a cabin pressurization malfunction during the climb in mountainous terrain; and were not able to control the cabin. The crew diverted to an alternate airport and landed safely.
Synopsis
G-IV crew reported a cabin pressurization malfunction during the climb in mountainous terrain; and were not able to control the cabin. The crew diverted to an alternate airport and landed safely.
Narrative
Aircraft was returned from maintenance after crew reported flaps failing to extend on final on the previous flight 2.5 days earlier. Crew reviewed maintenance records; performed full preflight inspection; and all checklist procedures with no issues. Crew performed a normal takeoff and departure from Runway XX on the departure up to 15000 ft. MSL. While climbing through 12000 ft. MSL aircraft indicated Cabin Pressure Manual; followed quickly by Cabin pressure low; and cabin oxygen on EICAS indications. Crew donned oxygen and continued climb to 15000 ft. to get above terrain and requested to remain at 15000 ft. with ATC to troubleshoot. Crew conducted checklists from the aircraft QRH and were unable to recover the pressurization system. Crew assessed that a divert to ZZZ1 was the best option that was closest; with a long runway; with no significant terrain and requested vectors and step down altitudes from ATC to get below 10;000 ft. as soon as possible in mountainous terrain. Crew then assessed it was necessary to [request priority] while on vectors and awaiting lower altitude assignment. On final to landing the crew experienced a repeat of the previous flaps failing to extend to the full landing position and assessed it was safe to continue to landing.
Second reporter narrative
Departing from ZZZ on Runway XX; departure required climb to 15k feet due to terrain. We were climbing at approximately 3000 feet/min in order to clear terrain. Climbing through approx 10000 feet; we received a cabin pres manual caution light; followed by cabin pressure low warning light; and then cabin oxygen on caution light. The cabin differential pressure never got above 0.05. We followed the QRH checklist. We tried different modes for the pressure controller. None of the modes fixed the cabin pressure. While troubleshooting; we stayed at 15;000 feet while starting a turn to the east. We were unable to descend lower due to high terrain west of ZZZ. After referencing and following all QRH procedures and guidance; we elected to [request priority]; donned oxygen masks; and elected to divert to ZZZ1. We had to climb to 16;000 feet for terrain and the cabin altitude reached a high of 16;300 feet. We also experienced severe turbulence and icing as we were IMC at 16;000 feet. The approach and landing at ZZZ1 (Runway XYL) was uneventful. Cause: Unknown. All preflight checks were accomplished normally and all switches were in normal operating modes. Suggestions: Unknown as cause of event is unknown.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.